1. Field of the invention
The present invention generally relates to an apparatus and process for manufacturing a rectangular-wire coil, and more particularly to an apparatus and simple process for manufacturing a rectangular-wire coil simply at a low cost.
2. Description of the Related Art
Development of electric and hybrid cars has been emphasized as one way to address the need to reduce particle and noise pollution. Development of high-performance motor to be mounted on such a car mentioned above has also proceeded. As coils for such motors, those using circular cross-section enameled wire and those using rectangular enameled wire are both well known.
The circular cross-section enameled wire provides an advantage of that a raw material of wire is low-cost on one hand but has a disadvantage of that the fill factor of a motor is limited, the fill factor of a motor being the ratio of "a sum total of cross-sectional areas of all the coil wire in a slot" to "a cross-sectional area of a slot in a motor body". Motor performance should increase as is increased motor fill factor.
Rectangular enameled wire is enameled wire which has a rectangular cross sectional shape. Using the rectangular enameled wire reduces the clearance between enameled wire in a slot of a motor, so that it becomes possible to increase fill factor of a motor and improve motor performance. From a practical point of view, fill factor of the rectangular enameled wire is generally 70-80%, in contrast to that of the circular cross-section enameled wire which is 30-50%.
For example, an apparatus for manufacturing a coil, shown in Japanese Patent Laid-Open Publication No. Hei 7-183152, is comprised of a bobbin on which rectangular wire is wound, a reduction roll to correct torsion set of the rectangular wire, and a winding form to take up the corrected rectangular wire, wherein a coil is formed by winding the rectangular wire on the winding form.
By using a rectangular-wire coil as mentioned above, it becomes possible to improve the fill factor of a motor. However, this presents a problem that the cost of a motor becomes high since the cost of rectangular enameled wire that is a raw material of the rectangular-wire coil is high. The high cost of such wire mainly derives from factors such as its manufacturing process being more complicated than that of circular cross-section enameled wire, uniform coating of resin around wire shaped rectangular in cross section is difficult, or the like. The cost of rectangular enameled wire is now actually two or more times that of circular cross-section enameled wire.
Attempts have been made to prepare a bobbin wound by the rectangular wire and form a coil using the rectangular wire pulled out of the bobbin as shown in above-mentioned Japanese Patent Laid-Open Publication No. Hei 7-183152. Torsion set, however, appears when the rectangular wire is wound on the bobbin. The remaining torsion set causes the shape of the completed coil to be less accurate, sets torsion on the rectangular wire, and creates clearance between the rectangular wire. It is therefore necessary to provide a reduction roll for removing the torsion set in the art described above. Such construction complicates the manufacturing process and apparatus and causes to motor cost to increase.